The present invention relates generally to a high speed mailing machine which includes a postage meter for applying a postage indicia to mail pieces passing through the machine. More particularly, the present invention relates to an improved inking device in the postage meter for continuously applying ink to the printing die of the meter.
In a typical high speed mailing machine, mail pieces usually in the form of envelopes, are fed seriatim along a feed deck by suitable feeding devices past a plurality of working stations which usually include an envelope flap opening device, a flap moistening device, a flap closing and sealing device, a postage meter, and a stacking device. The mailing machine may also include a scale for weighing the mail pieces before they pass through the postage meter. A principal advantage of such machines is that they can perform the aforementioned operations on mail pieces at a very high rate of speed, typically about three to four mail pieces per second, and therefore are very attractive to high volume mailers such as credit institutions, telephone companies, telemarketing operations, etc.
One of the limiting factors in maintaining high speed operation of such mailing machines is the speed with which the printing die of the postage meter can be reinked after each cycle of operation. Reinking after each printing cycle is necessary in order to consistently print a sharp, uniform indicia on each envelope which will pass the rigid print quality standards of the U.S. Postal Service. Thus, during each printing cycle, the printing die of the postage meter is inked by an inking device which normally is disposed in a home position, and which s extended laterally to an operative position. In this position, the inking device is moved upwardly to press against the underside of the printing die which applies the postage indicia to the envelopes as they are fed through the postage meter. Immediately after being pressed against the printing die, the inking device is lowered and retracted to its home position, after which the printing operation takes place. Thus, during each cycle of operation, the inking device moves from a home position laterally of the direction of envelope movement to the operative position, then upwardly to ink the printing die, then downwardly, and finally laterally back to the home position.
When it is considered that the mailing machine with which the present invention is concerned is capable of handling as many as four mail pieces per second, it becomes apparent that the foregoing cycle of operation of the inking device occurs at a very high rate of speed, with successive movements of the inking device being measured in milliseconds. A typical cycle of operation requires about 100 ms, of which only 40 ms are required for movement of the inking device, the other 60 ms occurring while the inking device is stationary. Thus, the movement of the inking device during each cycle of operation is characterized by extremely rapid acceleration and deceleration between successive increments of movement, as a result of which large acceleration and deceleration forces are imposed on the individual parts of the inking device. In fact, each acceleration and deceleration produces about three to four Gs of force on these parts, and even though the individual parts are of relatively small mass, the effect of these forces creates problems which are unacceptable from the standpoint of maintaining a functional postage indicia printing device.
It has been found through high speed photography that each time the inking device is accelerated and decelerated in the direction of lateral movement, the aforementioned forces are sufficient to laterally distort the ink pad along the front and rear edges thereof, which normally are in virtual contact with the adjacent inner edges of the walls of an ink reservoir in which the ink pad is disposed. When the ink pad is moved upwardly and pressed against the printing die, the ink pad is compressed, and the edges thereof are bulged upwardly and outwardly, with the result that the ink in the bulged edges of the pad is squeezed out onto the adjacent upper surface of a cover which secures the ink pad in an ink holding tray. If this were the sole movement of the ink pad, the ink which is squeezed out onto the adjacent upper surface of the cover would immediately be reabsorbed by the ink pad, although this could require about four to five seconds to occur. However, the rapid acceleration and deceleration of the inking device at the rate of four cycles per second does not leave sufficient time for the edges of the ink pad to reabsorb the ink squeezed onto the cover before the forces created by the rapid acceleration and deceleration cause the edge portions of the ink pad to distort in and outward direction, depending on whether the front or rear edge of the ink pad is being considered. This distortion tends to push the ink on the cover further away from the ink pad and thereby even further inhibit any reabsorption of the ink on the cover by the ink pad.
One solution to this problem would be to use an ink pad formed of a relatively stiff material which would not distort upon acceleration and deceleration, or bulge in response to compression from contact with the printing die. However, it is necessary to use a relatively flexible material so that the ink pad will conform as precisely as possible to the planarity of the surface of the printing die to assure an even application of the ink to the entire surface of the die in order to obtain the best possible print quality for the indicia. Although the amount of ink which is squeezed onto the lid during each cycle of operation is relatively small, after several tens of thousands of such cycles, sufficient ink is deposited on the lid to cause it to slosh onto other parts of the inking device and eventually to be deposited on envelopes as they are fed through the postage meter, thereby resulting either in partially illegible indicia or peripheral ink smudges elsewhere on the envelopes, or both, either of which is completely unacceptable. Thus, while the technical nature of the problem may seem relatively small, the operating requirements of the machine in which the problem occurs is such that the machine is not a commercially viable product so long as the problem exits.